It started as a popular uprising against the Syrian government, but it has become a lot more complicated, with nearly a dozen countries involved in two overlapping conflicts. (We explain it visually here: http://nyti.ms/1PuDp9Y)

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Syria vs. rebel groups

Rebel groups, including both ISIS and those supported by the U.S., are focused on toppling the Syrian president. Russia, Iran and the Lebanese group Hezbollah want to keep him in power, for now.

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U.S. vs. ISIS

The U.S. has been joined by Turkey, some rebel groups, and several Arab nations in its fight against ISIS. Syria and its allies (especially Russia) see ISIS as insurgents or terrorists and are fighting them as well.

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Kurdish fighters vs. ISIS

Here's where the overlapping conflicts start to get tricky: Kurdish ground forces have been America’s main partner in the war against ISIS in Syria. But that has increased tensions between the U.S. and Turkey, which has been fighting a bitter war with Kurdish separates.

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Turkey vs. Kurds

Turkey has attempted to hinder Kurdish advances in Syria and is bombing Kurdish rebels in its own territory — despite saying that Turkey shares the American and Kurdish goal of defeating ISIS.

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U.S. vs. Russia

Another set of conflicting interests. The U.S. and Russia are on opposite sides of the Syrian civil war, but they're nominal allies in the fight against ISIS. Russian airstrikes have hit Syrian rebel groups supported by the U.S. and its allies. Russian cruise missiles have crossed areas where American jets have been flying.

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Iran vs. Saudi Arabia

Iran and Hezbollah are Shiite allies of the Syrian government. They're fighting rebel groups supported by Saudi Arabia and other Sunni Arab nations.